arc: Do not construct RestrictionSet with empty restrictions bundle

The legacy device_policy_restrictions tag can be empty and the code
tries to construct a restriction set with the empty bundle which causes
a crash. The newer device_policy_local_restrictions parses correctly
with empty body because the parsing code avoids passing empty bundle to
the set. In this fix we're adding a check on the bundle emptiness before
constructing the restriction set with it.

Bug: 213364202
Test: replace the new tag with the legacy tag and verify that app
launches successfully

Change-Id: Ib8dbbb4a550c4309e2243bf0611bb6c8565c0e96